1. Field of the Invention
The present invention relates to a sewing device for sewing together base materials into a three-dimensional trim cover assembly which is for example used for forming a headrest or armrest for use on an automotive seat. In particular, the invention is directed to a sewing device capable of sewing together two base materials along with a strip of sealing material which includes a resin sealing tape or strip.
2. Description of Prior Arts
Many of armrests or headrests for use on automotive seat are formed by a typical process which comprises the steps of: sewing separate base materials together to form a three-dimensional trim cover assembly conforming to a predetermined shape of armrest or headrest; placing the thus-formed three-dimensional trim cover assembly in a foaming die; injecting a liquid foaming agent into the inside of the trim cover assembly; and curing that liquid foaming agent into an increased mass of foam padding filled therein.
Besides such armrest or headrest, generally stated, a resultant foamed product formed by the afore-stated foaming process is what is generally described as a foamed product integral with the trim cover assembly, which may be processed into any desired product or item for use on an automotive seat.
This kind of foamed product integral with trim cover assembly, such as armrest or headrest, has been with the problem that, during the foaming process, the liquid foaming agent is leaked out through pinholes formed by sewing needle in at least one sewn connection portion in the trim cover assembly which is preformed by sewing two separate base materials together.
Solution to the foregoing problem is by using a strip of sealing material, such as a resin sealing tape or strip, to seal the foregoing needle holes. Namely, at the step of sewing together two separate base materials, after having placed the two separate base materials on top of the other, a sewing machine is operated to sew the strip of sealing material (preferably, a resin sealing tape) with the juxtaposed two base materials along a predetermined sewing line, so that particular localized parts of the strip of sealing material are forcibly inserted together with a thread in the respective pinholes being formed by sewing needle and through the two juxtaposed base materials, thereby sealing each of the pinholes and finally producing a sealed three-dimensional trim cover assembly. Hence, subsequent thereto, at foaming steps, a liquid foaming agent injected in the trim cover assembly is assuredly prevented by the thus-sewn strip of sealing material from being leaked out through the pinholes.
However, such strip of sealing material per se is quite small in width and assumes a very narrow strip or tape. As a result, certainly, the two juxtaposed base materials can be set at a given sewing point by simply abutting all the edges of the base materials against a guide member and be easily sewn with each other, with a constant margin to seam, but, it is difficult to precisely set and retain such narrow sealing material at a given sewing point upon the top of those base materials. It is therefore actually impossible to precisely sew the sealing material with the two base materials along such constant margin to seam.
Further, in the case that the strip of sealing material underlies the two base materials, the strip of sealing material per se is not viewed and can in no way be positioned at the given sewing point, as a result of which, it is impossible to precisely sew the sealing material with the base materials along a predetermined sewing path or line.